Why Don't Electric Fuel Pumps Catch Fire?

To expand on Sceptics explaination - to achieve combustion (sustained chemical reaction), you need:

- Fuel

- Air

- Heat

See http://en.wikipedia.org/wiki/Fire

So even if you get bubbles through the fuel tank and happen to acheive the perfect fuel-oxygen ratio inside the bubble, there is not enough heat from the motor to achieve ignition.

In the case of the arcing wire under the fuel, you may have had the fuel and the heat, but no oxygen.

You'll notice that nowadays most fuel pumps are in the fuel tank and "push" the fuel at pressure to the enging rather than "pulling" from the tank. Being in the tank the fuel pump is cooled by the gasoline and since it is under the fuel there is no oxygen near it to support combustion. Even if there is a dead short at the pump I've never seen any explosion or fire.

We were plagued by what appeared to be a fuel starvation problem in my Eclipse AWD road race car. On long lefts, it would cough and starve for fuel. We pulled the tank to install baffles when we discovered that the problem really was the electric fuel pump. The power connection had come loose and, on hard lefts, the wire would pull away from the terminal and arc! We could see evidence of arcing at the terminal. We tightened everything back down, and the fuel starvation went away. Point is, even with an electrical arc in the gas tank, it didn't catch fire. Good thing, eh? Otherwise, KABOOM!

You beat me Sceptic! GA

Well, the answers here are interesting because I remember when Flight TWA 800 exploded out of New York they blamed an electrical short.

This from Wikipedia;

"The NTSB investigation ended with the adoption of its final report on August 23, 2000. In it they concluded that the probable cause of the accident was an explosion of the center wing fuel tank, most likely as a result of faulty wiring."

Since the plane had just taken off from NY then the fuel tanks were most likely full so there should have been no air in there to cause an explosion.

Does that contradict what we learnt above?

As it was a short flight, they saved weight by not filling that tank. I forget now if they also had other tanks unfilled.

They were unlucky enough to have sufficient fuel in with the air to be within the flammability limits and simultaneously they got a short to ignite it.

The flight was from NY to Rome so it wasn't short.

Also, doesn't the premise that as soon as the fuel tank is emptied then it's prone to electrically derived explosion contradict everything said on here that the pump should always be immersed in the fuel in order to avoid it coming into contact with air, just in case there is such an electrical fault?

Since auto makers know how to do this it doesn't seem feasible that aircraft makers would design their rig so as to expose it to possible dangers, no matter what the circumstances.

Isn't the fuel in jets more flammable than gasoline used in cars? Do airliners have a pump in each tank? The report didn't say the fuel pump caused the problem is said a electrical short caused the problem. I imagine there are quite a few electrical source even in the wings near the tanks. And maybe a small leak in a fuel line near a electrical junction that wasn't tight enough. I imagine the equiptment in the wings of these aricraft takes quite a beating on every flight and the breif little inspection they get between flights (if they even get an inspection of any sort) wouldn't pick up a small leak or a lose connection.

Re: "Isn't the fuel in jets more flammable than gasoline..."

There are many different types of jet engines, which (collectively) burn a number of different fuels... Jet-A / JP4 / kerosene, etc.

I think JP4 is a mixture of gasoline and kero...(?) Anyway, I think the answer to your query is "No", if you're talking about plain-old-flammability-at-normal-atm-press/temp.

Surely there must be a thread here somewhere, comparing different fuels...?

The flight from NY to Rome is short compared to the range of a 747. After you try the Chicago - Narita run for 13 hours you know what short is.

In a car the fuel pump pulls gas out of the tank and into the motor / impeller housing and thence to the fuel line. The motor case separates the electrical parts from the fuel / air mixture in the tank itself and the liquid in the motor suppresses any sparks in the motor.

The spark in the TWA 747 was caused by harness chafe from a harness in the tank. The tank was mostly empty because the 747 didn't need that much fuel to get to Rome and an empty center tank keeps the plane in trim better than emptying the left wing tank.

I don't know why a plane would have a harness in the tank. Maybe there is somebody in the aviation business who knows.

I suspect the guy with the Eclipse was lucky. If it had been my Renault Fuego (that's Spanish for "fire" and very appropriate) the whole thing would have gone sky high...

Correct, planes only take on what is needed and a small reserve, it did not need to be full....even for Rome.

When a fuel tanks fuel is used the expended fuel must be replaced by something so there was probably air in the tank.

Well in my opinion it depends upon what the fuel was- sure it was not petrol!-(kerosene/ oxy mix?). On another tack, remember when my car stopped dead next to a petrol station( electric pump in tank< had 3/4 tank of petrol)- soon established pump not working(not rotating)- petrol station flatly refused me to lower petrol out of tank to enable removal of pump on grounds of explosion danger to others- auto lec offered to sell me external elec pump for 130 dollars- my auto club refused to transport me &car home(50kms) on grounds I was already where fault could be fixed-stinking hot summer day-anyway cost me $85 to get car trailored home. Next morning, lifted boot lid, then somehow or other,I thought what if I just thump tank next to pump with my hand- did so- & the @#$%^& pump worked & stayed working for the rest of the time I had that car(about 8 years!).

The fuel tank in question was not full, it was almost empty......air was also in abundance inside....the air conditioning used the fuel to keep cool, due to the lack of fuel in that tank, the small amount of fuel was "overheated".

You should try and find the good TV program on the reasons for the explosion. I saw it last year on N-TV here in Germany....try YouTube maybe.....

Nobody has mentioned car fuel gauge "Sender" units!! Which are a completely open wire resistance with a moveable wiper attached to a float!!! Sparks galore!!! But no problems as the atmosphere inside the tank is 99% petrol, therefore it cannot catch fire.....

40 years ago, Carl Ludvigson was the editor of what was then called Sports Cars Illustrated (Now it's called Car & Driver).

We met at the Hartford Auto Show where he was demonstrating a halon fire extnguisher system that used NASA developed IR sensors and valves. It was a commercial adaptation of a passive system he helped develop for use in race cars. To say that the system was impressive is a gross understatement.

In discussing fire suppression systems, Carl explained that during world war 2, most of the losses of allied bombers occured on the return trip from the bombing run. Full wing tanks did not catch fire or explode when hit by enemy fire but in the return trip, the empty or partially filled tanks were rich in fumes and oxygen sufficient to be ignited by the slightest spark.

Such losses were substantially minimized when someone suggested that they put out the fires by flooding the damaged tank with gasoline from another tank!

A suggestion such as this must have been viewed as the rantings of a maniac. Those who were desperate enough to try it must have felt like the first person to ever eat a lobster but when your plane is on fire, what have you got to loose?!

I first saw a submerged fuel pump in the tank of a Jaguar 4 door "saloon" (how do they come up with such names?). I peered down into the tank through the open filler door and there sat the Lucas pump, brushes sparking merrily away while submerged in gasoline! That was circa 1960, and like most of you, the sight startled me.

If there was any danger to the installation it was more likely caused by who made the pump, not the concept used.

L.J.

My uncle once told me that when he was a machinist in the 1940s, they kept open tanks of gasoline sitting around the shop for cleaning parts. A "rite of manhood" was to extinghuish lit cigarettes in the gasoline. The trick was to do it fast enough so the lit part didn't ignite the vapor hovering over the gasoline.

(My "rite of manhood" was walking under a 40-ton nuclear reactor vessel being carried by an overhead crane out of the Babcock & Wilcox fabrication plant in Mount Vernon, Indiana, to a barge in the Ohio river. Dozens of guys would scurry under the vessel, no matter how many rules there were against it. But I digress.)

I also remember a pro rally Datsun 510 that split its gas tank because the rear strut towers collapsed on it after blasting down a particularly nasty forest road in Michigan, filled with strut busters, bunyip crossings and rockadillos. The service crew used a hydraulic jack to push the struts back into place, pulled the tank, welded it up, and put it back in, but it continued to leak. Gasoline was sloshing around the floorboards, but the team pressed on through the night until the navigator finally got out of the car and declared he was no longer going to ride in a mobile bomb. Considering that those cars ran about 60 amps of driving lights up front and the battery cables ran from the back of the car through the interior, it's a wonder that the lil 510 didn't explode somewhere in the Michigan woods.

*sigh* Nostalgia just isn't what it used to be.

Slow Old Poop wrote: "The service crew used a hydraulic jack to push the struts back into place, pulled the tank, welded it up, and put it back in. . "

It's a wonder the tank didn't blow during welding. I remember a radiator repair facility in NY City in the 60's. Their business was mostly replacing radiator cores but they also had a submersion vat for cleansing fuel tanks prior to welding.

One day the owner was not to be seen. Eight weeks later, he showed up looking as if he'd fallen into a sewing machine.

The story was that he attempted to weld a seam on a gas tank that had soaked for three days in the vat. Apparently, three days wasn't enough for the tank ruptured, not with an explosion so much as a really loud "Pop!". In ripping apart, the sheet metal caught the man in the rib cage, dug in and then traveled up his chest and across his face.

I never forgot that. In fact a few months back I posted an inquiry here at CR4 looking for advice on how to remove a dent in each of two motocycle tanks.

Between the responses and my experience, I left them alone.

L.J.

>It's a wonder the tank didn't blow during welding.

Pro rally service crews are used to doing the impossible in a very short time. As I recall, they strapped two five-gallon gas cans to the roll cage in the rally car (not mine) whilst they took the tank to a local garage. They filled the tank with water, welded it up with water in it (which is why it probably didn't last long), and re-installed it at the next service halt.

As an example of what a service crew can do under pressure: I came into a midnight service halt with my rally car and told the crew: "The battery cables are loose and jumping off the terminals, the down pipe fell off the exhaust manifold, and the throttle return spring is broken. Please fix it whilst we go inside and eat." They did, too.

In 1962 the Formula One GP of the United states was still being held at Watkins Glen, NY. I was flattered and privilged to be invited by Rob Walker to be a member of his crew. I got to watch entire teams in action, not just ours but BRM, Lotus, McLaren, et al.

Ferrari was not in the points lead for the constructors championship or the drivers championship so they simply chose not to show up! It would have been entertaining to say the least as their pit stops where charcterized as Italian variations on Chinese Fire drills.

Even without Ferrari, the grand Prix was an experience over which I will never get. I know, better than most, the pressures and skills that pit crews deal with.

And I miss Rob Walker terribly. While the current McLarens are supported by and bear a logo of the Walker distillery, his presence is sorely missed. He was a soft spoken, unprentious man of great generosity. A real gentleman who gave meaning to the term. He epitomized the sporting nature of the sport that has since been ruined by megabuck drivers driving exaggerated technology and dominated by the interests of car companies.

But that is another converstion.

L.J.

I was there too, but as a spectator. I got to watch the fans burn a bus and play in the mud bog. No wonder F1 never came back.

My 1953 MG TD gas tank is weeping from pin-holes on the bottom, and I've pulled it and am awaiting delivery of cleaning and sealing materials. Sealing the inside of the tank requires removal of the sending unit which would be gummed up by the sealant. Bear in mind that the TD had no gas guage, only a warning light on the dash. Consequently the sending unit is merely a float attached to an arm which, inside the sending unit becomes one side of a simple switch. When the gasoline level and the float drop to a certain point, the contacts inside the sending unit meet, completing a simple series circuit to the warning light on the dash. This is confirmed by the MG wiring diagram. So you have, inside the gas tank (and inside the sending unit body), a simple blade switch conducting 12 volts in series with a small lamp. There must be a tiny spark when those contacts meet, and granted, if the chamber inside the sending unit is filled with gasoline there would be no oxygen for combustion. But there's no provision to assure that the sending unit is filled with gasoline. The float arm simply runs through a hole in the side of the sending unit so, eventually, fuel would get inside it. But what about that moment when the fuel and air mix is optimal and the switch sparks? Apparently time has proved it's not a problem, but who knew?